class TestSequence is Sequence {
  construct new() {}

  iterate(iterator) {
    if (iterator == null) return 1
    if (iterator == 3) return false
    return iterator + 1
  }

  iteratorValue(iterator) { iterator }
}

var test = TestSequence.new().skip(0)

System.print(test is Sequence) // expect: true
System.print(test) // expect: instance of SkipSequence

// Skipping 0 changes nothing.
System.print(test.toList) // expect: [1, 2, 3]

// Skipping 1 works.
System.print(test.skip(1).toList) // expect: [2, 3]

// Skipping more than length of sequence produces empty list.
System.print(test.skip(4).isEmpty) // expect: true